This invention relates generally to phase shifters, and, more particularly, to phase shifters of the kind that are aligned with the inner conductor of a transverse electromagnetic (TEM) transmission line.
It is frequently necessary to shift the phase of signals being transmitted along a TEM transmission line. Equalizing the signals output by a hybrid coupler, for example, usually requires a differential phase shifting of one output branch. In the past, phase shifting of this kind has sometimes been provided by incorporating an excess line length in a particular one of the output branches. This is not an entirely satisfactory technique, however, because an excess line length is dispersive, i.e., it provides a phase shift that is directly proportional to frequency.
Other phase shifters of this kind used in the past have included elements that are not aligned with the transmission line. Although generally effective at shifting the phase of the transmitted signal, without introducing excessive dispersion, such phase shifters are believed to be excessively bulky. In addition, these phase shifters require modification of both the inner and outer conductors of the transmission line.
It should be appreciated that there is a need for a phase shifter for use in a TEM transmission line, which is aligned with the line's inner conductor, such that the outer conductor can remain unmodified, and which provides convenient selection of the amount of phase shifting, while providing low dispersion. The present invention fulfills this need.